Traditionally, of course, falcons have been classified with other diurnal raptors, parrots have been positioned between doves and cuckoos, and seriemas have been lumped with cranes, rails, and other birds in the order Gruiformes. (If you’re not familiar with the South American seriemas, here’s a great image. I like this one too.)

However, evidence has mounted in recent years that falcons are not closely related to other diurnal raptors and seriemas don’t belong anywhere near gruiform birds. In fact, the two groups appear to belong near parrots and passerines, which are now thought to be sister clades.

Some of this should sound familiar. A couple of well-publicized studies, including the “Early Bird” project, have presented these hypotheses in recent years, leading several checklist authorities, including the AOU, Clements, and IOC World Bird List, to move seriemas into their own order (Cariamiformes) and to restrict Falconiformes to falcons, moving hawks, eagles, kites, and other diurnal raptors to an order called Accipitriformes.

But what no major checklist has yet done (to my knowledge) is to take the next step and rearrange the order in which these groups of birds are presented. Even the generally progressive IOC World Bird List has as of this writing has a footnote saying, “Will resequence in the future.” It’s all well and good to erect new orders while leaving the sequence more or less the same, but moving parrots next to passerines and putting seriemas and falcons nearby, far from the birds they much more strongly resemble? That’s a big step, and it’s going to throw a lot of people for a loop.

Proposition 491, though, could be the start of a sea change if it passes, or even just by virtue of its introduction. The AOU North American committee could go through its own review process as early as next year, Clements would follow in short order if that passed, and the IOC list would almost certainly make similar changes somewhere along the way. Some field guides would eventually follow as well, though I think changes like this could start driving more field guide authors and publishers away from following strict taxonomic order. Separating ducks and coots is one thing, but separating hawks and falcons? I think that would be a tough sell.

It’s exciting and mind-bending to ponder a seriema-falcon-parrot-passerine relationship. Seriemas are long-legged terrestrial hunters related to extinct terror birds (phorusrhacids). Parrots have bills that certainly seem raptorial – consider the bills of a macaw or a kea, a caracara, and Titanis. Then of course there are the wood-warblers, carnivores after a fashion but without any of the heavy equipment.

The problem is that we can’t tell what the physical characteristics actually indicate about these relationships (yet). “No morphological characters are known that convincingly support a Passeriformes / Psittaciformes clade,” wrote Gerald Mayr in a recent review, not suggesting that the hypothesized relationship is necessarily incorrect but simply that so far at least, no known physical characteristics back up what genetics work is telling us. (A group of birds known only from fossils, however, appears to be very close to passerines but shares the foot shape of parrots rather than living passerines.) So comparisons of bill shapes, foot shapes, and the like can certainly stimulate the imagination, but we need rigorous science to explore and synthesize more molecular work, morphological analysis, and biogeographical hypotheses in order to close more gaps in our understanding.

The SACC will have to determine whether they believe there’s strong enough evidence to make these changes now, or whether to wait for additional published research before making such significant sequence changes. Interestingly, Proposal 491 didn’t initially present any new information, citing studies from 2006 and 2008. However, comments from Keith Barker appended to the proposal cite additional support forthcoming for the parrot-passerine relationship and make the suggestion that seriemas also be moved. (Dr. Barker has been involved in important avian systematics projects, including the paper responsible for the recent wood-warbler overhaul.) I think this proposal has a good shot at passing, at least in South America. What do you think? Is it too soon to make changes this big, or is the evidence strong enough to proceed? And would you use a field guide that splits up hawks and falcons?

David J. Ringer is exploring the world one bird at a time. His fascination with birds and nature began at the age of four or five, and he now works full time in conservation. He is a writer and communicator whose day jobs have taken him to six continents and more than 25 countries, including Papua New Guinea, Vanuatu, Kenya, and Cameroon. Follow him on Twitter at @RealDJRinger.

Birders, especially young birders, learn a lot of their “bird science” from field guides, perusing them, turning the pages and absorbing what is there. I always figured that what came first in the field guide came first in evolution, too. Surely a loon looks something like the Cretaceous bird, Hesperornis, so putting loons at the beginning made sense. And aren’t sparrows pretty smart? Especially House Sparrows. Yeah, they could go at the end.

A comfortabe picture until Sibley, Ahlquist and Monroe came along with their DNA and screwed it all up. The problem with field guides is that when you need one in the field, you often need it fast. Changing the order of everything with each edition might be scientifically correct, but it makes it tough when you need to see a Philadelphia Vireo image right now, and it’s moved from before the warblers to after the flycatchers, and where the hell is it going to be next time.

Perhaps we need a commission to establish a standard “field guide order” and put the science in an appendix.

James and Steve – it’s a dilemma. As Greg Laden said in response to this post, and to your point, Steve, it’s important for people to learn about birds’ phylogenetic relationships and the larger implications thereof. On the other hand, a book that has flamingos next to grebes, falcons next to parrots, and swifts next to nightjars, is hardly ID-friendly for people not already familiar with all the major orders, families, and even genera they are likely to encounter on a birding trip (or in their backyards). As a matter of fact, Steve N. G. Howell et al. published an article in Birding proposing a “field-friendly sequence” for field guides, which met with mixed reviews but makes some good points.

[…] (Passeriformes), more closely to reflect the relationships between these three great orders. I wrote about this last year. South American seriemas also belong with this newly recognized group, as explained in my earlier […]